During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three...During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three-dimensional(3 D)vertical stress model,which ignores the effect of mine depth,failing to obtain the vertical stress at different positions along stope length.Therefore,this paper develops and validates an improved 3 D model solution through numerical simulation in Rhino-FLAC^(3D),and examines the stress state and stability of backfill under different conditions.The results show that the improved model can accurately calculate the vertical stress at different mine depths and positions along stope length.The error rates between the results of the improved model and numerical simulation are below 4%,indicating high reliability and applicability.The maximum vertical stress(σ_(zz,max))in backfill is positively correlated with the degree of rock-backfill closure,which is enhanced by mine depth and elastic modulus of backfill,while weakened by stope width and inclination,backfill friction angle,and elastic modulus of rock mass.Theσ_(zz,max)reaches its peak when the stope length is 150 m,whileσ_(zz,max)is insensitive to changes in rock-backfill interface parameters.In all cases,the backfill stability can be improved by reducingσ_(zz,max).The results provide theoretical guidance for the backfill strength design and the safe and efficient recovery of ore pillars in deep mining.展开更多
In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock j...In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.展开更多
The normal compression tests on intact samples and artificial joints with different saw-tooth shape under cyclic loading and half-sine waves of different frequencies were performed by using Instron1342 servo-controlle...The normal compression tests on intact samples and artificial joints with different saw-tooth shape under cyclic loading and half-sine waves of different frequencies were performed by using Instron1342 servo-controlled material testing machine. The specimens were made artificially with mortar. The loading frequency ranged from 0.005 Hz to 0.1 Hz. The experimental results show that joint closure curves are non-linear and concave up. The stress-deformation curves under cyclic loading exhibit hysteresis and permanent set that diminish rapidly and keep constant finally on successive cycles. Normal displacement successively decreases from the joint J1 to J2, to J3 under the same normal loads regardless of frequency. Considering the loading frequency effect, normal displacement of joint J1 decreases with increasing the loading frequency except that the loading frequency is 0.05 Hz. Normal displacement of joint J2 increases with increasing the loading frequency. Normal displacement of joint J3 increases with increasing the loading frequency when the frequency ranges from 0.005 Hz to 0.05 Hz. Its normal displacement, however, becomes least when the loading frequency is 0.1 Hz.展开更多
Objective BACKGROUND Spontaneous closure of direct traumatic carotid cavernous fistulas (TCCFs) is rare. A few cases have been reported in literature to be related to diagnostic cerebral angiography and orbital venogr...Objective BACKGROUND Spontaneous closure of direct traumatic carotid cavernous fistulas (TCCFs) is rare. A few cases have been reported in literature to be related to diagnostic cerebral angiography and orbital venography. Several mechanisms have been postulated, including irritation of the vessels from contrast media, compression of the carotid artery and reduced blood pressure from general anesthesia. In our own series of about 400 patients at Ramathibodi Hospital, the incidence is approximately 1.75%.CASE PRESENTATION We present a case, which spontaneous closure occurred during attempted endovascular embolization. A 45-year-old woman with left TCCF was referred to our hospital for endovascular treatment. Cerebral angiogram revealed a small-hole fistula at the posterosuperior wall of C2-3 segment of the LICA. Transarterial balloon failed due to the small size of the fistula and acute retroangulation of the balloon attached microcatheter. Transarterial GDC coil placement into the first venous pouch was then attempted for two times, but was unsuccessful. During repositioning of the microcatheter for a third attempt, spontaneous closure of the fistula was observed and confirmed by control angiogram. CONCLUSION Spontaneous closure of direct traumatic carotid cavernous fistulas may occur during endovascular procedures, which can be caused by dissection of the venous pouch by the microcatheter or coils during manipulation, irritation of the vascular walls from the contrast media and decreased blood pressure from general anesthesia.展开更多
Background It’s essential to prevent from thrombosis on device without increasing the risk of bleeding complications after successfully implanted left atrial appendage device.At present,no guidelines recommend about ...Background It’s essential to prevent from thrombosis on device without increasing the risk of bleeding complications after successfully implanted left atrial appendage device.At present,no guidelines recommend about postoperative antithrombotic therapy of left atrial appendage closure(LAAC).The purpose of this study is to investigate the safety and efficacy of different antithrombotic therapies after LAAC.展开更多
Background Cryoballoon ablation has been demonstrated to be an effective way for the treatment of atrial fibrilation(AF).However,in the population with high risk of thromboembolism,long-term oral anticoagulants are st...Background Cryoballoon ablation has been demonstrated to be an effective way for the treatment of atrial fibrilation(AF).However,in the population with high risk of thromboembolism,long-term oral anticoagulants are still in need,which lead to the odds of hemorrhage.As previous studies confirmed,left atrial appendage closure(LAAC)could decrease the risk of thromboembolism in AF patients,and may substitute for the long term anticoagulation.Therefore,we attempted to combine both these operations for AF.展开更多
China has embarked on an extensive and sustained endeavor to harness its coal resources for a substantial period.However,the depletion of coal reserves in mining regions has necessitated the closure or abandonment of ...China has embarked on an extensive and sustained endeavor to harness its coal resources for a substantial period.However,the depletion of coal reserves in mining regions has necessitated the closure or abandonment of numerous mines,resulting in a marked increase in the number of such facilities.Parallel to this,China is vigorously advancing the development of a novel energy power system,aimed at transitioning the power sector from a high-carbon,fossil fuel-dependent paradigm to a low-carbon,clean energy footing.展开更多
In this paper,we present a new method of intelligent back analysis(IBA)using grey Verhulst model(GVM)to identify geotechnical parameters of rock mass surrounding tunnel,and validate it via a test for a main openings o...In this paper,we present a new method of intelligent back analysis(IBA)using grey Verhulst model(GVM)to identify geotechnical parameters of rock mass surrounding tunnel,and validate it via a test for a main openings of−600 m level in Coal Mine“6.13”,Democratic People's Republic of Korea.The displacement components used for back analysis are the crown settlement and sidewalls convergence monitored at the end of the openings excavation,and the final closures predicted by GVM.The non-linear relation between displacements and back analysis parameters was obtained by artificial neural network(ANN)and Burger-creep viscoplastic(CVISC)model of FLAC3D.Then,the optimal parameters were determined for rock mass surrounding tunnel by genetic algorithm(GA)with both groups of measured displacements at the end of the final excavation and closures predicted by GVM.The maximum absolute error(MAE)and standard deviation(Std)between calculated displacements by numerical simulation with back analysis parameters and in situ ones were less than 6 and 2 mm,respectively.Therefore,it was found that the proposed method could be successfully applied to determining design parameters and stability for tunnels and underground cavities,as well as mine openings and stopes.展开更多
基金Project(2024ZD1003704)supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project,ChinaProjects(51834001,52130404)supported by the National Natural Science Foundation of China。
文摘During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three-dimensional(3 D)vertical stress model,which ignores the effect of mine depth,failing to obtain the vertical stress at different positions along stope length.Therefore,this paper develops and validates an improved 3 D model solution through numerical simulation in Rhino-FLAC^(3D),and examines the stress state and stability of backfill under different conditions.The results show that the improved model can accurately calculate the vertical stress at different mine depths and positions along stope length.The error rates between the results of the improved model and numerical simulation are below 4%,indicating high reliability and applicability.The maximum vertical stress(σ_(zz,max))in backfill is positively correlated with the degree of rock-backfill closure,which is enhanced by mine depth and elastic modulus of backfill,while weakened by stope width and inclination,backfill friction angle,and elastic modulus of rock mass.Theσ_(zz,max)reaches its peak when the stope length is 150 m,whileσ_(zz,max)is insensitive to changes in rock-backfill interface parameters.In all cases,the backfill stability can be improved by reducingσ_(zz,max).The results provide theoretical guidance for the backfill strength design and the safe and efficient recovery of ore pillars in deep mining.
基金Project(51274249)supported by the National Natural Science Foundation of ChinaProject(2015zzts076)supported by the Explore Research Fund for Graduate Students of ChinaProject(201406)supported by the Hunan Key Laboratory of Coal Resources and Safe Mining Open-end Funds,China
文摘In order to investigate the failure mechanism of rock joint,a series of laboratory tests including cyclic direct shear tests under constant normal load(CNL)conditions were conducted.Morphology parameters of the rock joint surface were precisely calculated by means of a three-dimensional laser scanning machine.All test results were analyzed to investigate the shear behavior and normal displacement behavior of rock joints under CNL conditions.Degradation of rock joint surface during cyclic shear tests was also analyzed.The comparison results of the height parameters and the hybrid parameters of the joint surface during cyclic tests show that the degradation of the surface mostly happens in the first shear and the constant normal loads imposed on the joints have significant promotion effects on the morphology degradation.During cyclic shear tests,joints surfaces evolve from rough state to smooth state but keep an overall undulation.Dilatancy of rock joints degrades with the degradation of joint surface and the increase of normal loads.The closure deformation of joint is larger than that of the intact rock,and the normal stiffness increases with the increase of shearing times.
基金Projects(50490274 50490272) supported by the National Natural Science Foundation of ChinaProject(2002CB412703) supported by theNational Basic Research Program of China
文摘The normal compression tests on intact samples and artificial joints with different saw-tooth shape under cyclic loading and half-sine waves of different frequencies were performed by using Instron1342 servo-controlled material testing machine. The specimens were made artificially with mortar. The loading frequency ranged from 0.005 Hz to 0.1 Hz. The experimental results show that joint closure curves are non-linear and concave up. The stress-deformation curves under cyclic loading exhibit hysteresis and permanent set that diminish rapidly and keep constant finally on successive cycles. Normal displacement successively decreases from the joint J1 to J2, to J3 under the same normal loads regardless of frequency. Considering the loading frequency effect, normal displacement of joint J1 decreases with increasing the loading frequency except that the loading frequency is 0.05 Hz. Normal displacement of joint J2 increases with increasing the loading frequency. Normal displacement of joint J3 increases with increasing the loading frequency when the frequency ranges from 0.005 Hz to 0.05 Hz. Its normal displacement, however, becomes least when the loading frequency is 0.1 Hz.
文摘Objective BACKGROUND Spontaneous closure of direct traumatic carotid cavernous fistulas (TCCFs) is rare. A few cases have been reported in literature to be related to diagnostic cerebral angiography and orbital venography. Several mechanisms have been postulated, including irritation of the vessels from contrast media, compression of the carotid artery and reduced blood pressure from general anesthesia. In our own series of about 400 patients at Ramathibodi Hospital, the incidence is approximately 1.75%.CASE PRESENTATION We present a case, which spontaneous closure occurred during attempted endovascular embolization. A 45-year-old woman with left TCCF was referred to our hospital for endovascular treatment. Cerebral angiogram revealed a small-hole fistula at the posterosuperior wall of C2-3 segment of the LICA. Transarterial balloon failed due to the small size of the fistula and acute retroangulation of the balloon attached microcatheter. Transarterial GDC coil placement into the first venous pouch was then attempted for two times, but was unsuccessful. During repositioning of the microcatheter for a third attempt, spontaneous closure of the fistula was observed and confirmed by control angiogram. CONCLUSION Spontaneous closure of direct traumatic carotid cavernous fistulas may occur during endovascular procedures, which can be caused by dissection of the venous pouch by the microcatheter or coils during manipulation, irritation of the vascular walls from the contrast media and decreased blood pressure from general anesthesia.
文摘Background It’s essential to prevent from thrombosis on device without increasing the risk of bleeding complications after successfully implanted left atrial appendage device.At present,no guidelines recommend about postoperative antithrombotic therapy of left atrial appendage closure(LAAC).The purpose of this study is to investigate the safety and efficacy of different antithrombotic therapies after LAAC.
文摘Background Cryoballoon ablation has been demonstrated to be an effective way for the treatment of atrial fibrilation(AF).However,in the population with high risk of thromboembolism,long-term oral anticoagulants are still in need,which lead to the odds of hemorrhage.As previous studies confirmed,left atrial appendage closure(LAAC)could decrease the risk of thromboembolism in AF patients,and may substitute for the long term anticoagulation.Therefore,we attempted to combine both these operations for AF.
文摘China has embarked on an extensive and sustained endeavor to harness its coal resources for a substantial period.However,the depletion of coal reserves in mining regions has necessitated the closure or abandonment of numerous mines,resulting in a marked increase in the number of such facilities.Parallel to this,China is vigorously advancing the development of a novel energy power system,aimed at transitioning the power sector from a high-carbon,fossil fuel-dependent paradigm to a low-carbon,clean energy footing.
基金Project(32-41)supported by the National Science and Technical Development Foundation of DPR of Korea。
文摘In this paper,we present a new method of intelligent back analysis(IBA)using grey Verhulst model(GVM)to identify geotechnical parameters of rock mass surrounding tunnel,and validate it via a test for a main openings of−600 m level in Coal Mine“6.13”,Democratic People's Republic of Korea.The displacement components used for back analysis are the crown settlement and sidewalls convergence monitored at the end of the openings excavation,and the final closures predicted by GVM.The non-linear relation between displacements and back analysis parameters was obtained by artificial neural network(ANN)and Burger-creep viscoplastic(CVISC)model of FLAC3D.Then,the optimal parameters were determined for rock mass surrounding tunnel by genetic algorithm(GA)with both groups of measured displacements at the end of the final excavation and closures predicted by GVM.The maximum absolute error(MAE)and standard deviation(Std)between calculated displacements by numerical simulation with back analysis parameters and in situ ones were less than 6 and 2 mm,respectively.Therefore,it was found that the proposed method could be successfully applied to determining design parameters and stability for tunnels and underground cavities,as well as mine openings and stopes.
